1. Field of the Invention
The present invention is a technology relating to exhaust gas treatment, specifically a technology relating to removal of hydrocarbon in exhaust gas.
The present invention can be used for treatment of industrial exhaust gas and treatment of exhaust gas from internal combustion engine.
2. Description of the Related Art
In the initiation of operation of an internal combustion, it is difficult to sufficiently treat exhaust gas using a usual catalyst for exhaust gas treatment because temperature of exhaust gas is low. To solve such a problem, an adsorbent for hydrocarbons (hereinafter, sometimes referred to as “HC”) using zeolite, which utilizes adsorbing property for hydrocarbons, has been used. Furthermore, a technology has been disclosed, which can be used as a catalyst for exhaust gas by combining an adsorbent for hydrocarbons and a catalyst for exhaust gas purification.
Regarding HC adsorption capacity of zeolite, a number of studies have been done and it has been shown that such types of zeolite as ZSM5 type, USY type, mordenite type, β type, and the like are preferable (see, for example, JP-A-7-241471). Also, JP-A-7-96177 discloses a technology to improve HC adsorption capacity of zeolite, by applying acid treatment to unmodified zeolite to obtain a heat-resistant zeolite followed by applying steam treatment thereto. Further, it has been indicated that aforementioned zeolite can be used as a catalyst for exhaust gas treatment by adding a catalytically active component thereto, and also it has been shown that zeolite and catalyst are each made laminar to exert individual effect separately in order to improve HC adsorption effect thereof (see, for example, JP-A-2004-8940 and JP-A-2-56247).
However, conventional types of zeolite have a room to be improved in view of thermal stability (durability) and HC adsorption capacity. In particular, such types of zeolite are poor in hydrothermal stability, and have a problem of durability when they are used in exhaust gas from engine as an adsorbent.
In addition, even those having superior durability, they sometimes cause problems in handling property or coating property when zeolite slurry is prepared, and an improvement has been demanded from the viewpoint of production efficiency.
Thus, an object of the present invention is to improve hydrocarbon-adsorbing property of zeolite when the zeolite is used as an adsorbent for hydrocarbons, and also to improve durability of the adsorbent.
In addition, another object of the present invention is to provide a zeolite superior in handling property in preparing slurry thereof.